Signal amplitude coders



July 19, 1966 D. R. BARBER SIGNAL AMPLITUDE coDERs Filed Sept. 6, 1965OONAL 0 R. BARBER United States Patent() 3,262,107 SIGNAL AMPLITUDECODERS Donald Robert Barber, London, England, assigner to InternationalStandard Electric Corporation, New York, N.Y., a corporation of Delawaret Filed Sept. 6, 1963, Ser. No. 307,200 Claims priority, applicationGreat Britain, Sept. 14, 1962, 35,183/62 4 Claims. (Cl. 340-345) Thisinvention relates to signal amplitude coders in which .a sample of asignal wave is quantized into one of n levels -and a code combination isgenerated representative of the quantized signal level.

In genera-l coders are either parallel coders or serial coders. In aparallel coder the signal is `quantized directly into ,one of n levelsand the digits of the code combination Iare generated in parallel. Theparallel coder requires one circuit per level and can generate any codecombination. In the serial coder the signal is successively compared toa reference level, in between each trial the signal has a 4fixed amountsubtracted trom it or it is divided by a fixed ratio. The digits of thecode combination are generated serially, digit by digit during eachtrial. The serial coder requires only one circuit per digit but has thedisadvantage that each circuit has to operate at a speed considerably inexcess of the digit rate. The serial coder can only generate certaincode combinations, for example a simple binary code.

According to the invention apparatus (for quantizing and coding anamplitude sample lof a signal wave comprises -a plurality of quantizingmeans arranged in succession, a connection for applying the signalsample to the input of the first `quantizing means, means forsubtracting the quantizing output of each quantizing means -frorn theinput thereto and applying the dilierence so obtained to the input ofthe next succeeding quantizing means, and a plurality of coding meanseach individual to a quantizin-g means for coding the quantized outputthereof.

In a preferred embodiment of the invention apparatus for quantizing andcoding an amplitude sample of a signal wave, where the sample is to bequantized into one of n amplitude levels, comprises first and secondquantizing means each capable of quantizing a signal sample into one of\/n levels, a `connection for applying the sig-nal sample to the inputof the first quantizing means, means for subtracting the quantizedoutput thereof =from the input thereto and applying the difference soobtained to the input of the second quantizing means, and coding meansindividual to each quantizing means yfor coding the quantized outputthereof.

The invention will .be best understood by reference to the `followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings wherein FIG. 1 is a block diagram of a coderusing two quantizing and coding stages; and

lFIG. 2 is a block dia-gram of a coder using a single quantizing andcoding stage in a reflex circuit.

In lFIG. 1 the signal S is first quantized into one of Vif levels by thefirst quantizer. The output of the first quantizer is coded by theIfirst coder. The output of the firs-t quantizer is also applied to asecondary signal generator which generates a secondary signal S1 at alevel equal to that level to which the incoming signal S was quantized.The secondary signal S1 is then subtracted fro-m the incoming signal Sby the subtract circuit, and the difference so obtained is passed to thesec- 7 ond quantizer, which also has Vn levels. The output from thesecond quantizer is coded by the second coder.

ice

In a typical example a signal sample corresponding to level 34 has to becoded in a 100-level system. The signal is first quantized in a l0-levelquantizer, and the coded Output indicates that the signal level is inthe 3() range. The quantized output vfrom the irst qu-antizer is fed tothe signal generator which produces a secondary signal equal to level30. This secondary signal is then subtracted from the original signal,providing a different signal equal to level 4 within the range 30 to 39.This diierence sigvnal is then quantized in the second 10-levelquantizer, the coded output of which indicates the level 4. The twocoded outputs Iare so arranged that the result is a code combinationrepresenting level 34.

This arrangement permits the use of two parallel coders, each havingonly 10 circuits `for coding a signal at 100 levels. Although the numberof circuits required is greater than that required by a serial coder,the speed of operation required of the circuits is approximately 1/2x(where x is the number of digits) slower than in the case of the serialcoder.

In the alternative arrangement shown in FIG. 2 the same quantizing andcoding apparatus is used for each v' quantizing and coding stage Iof thesignal. At the start of the sampling period gate G1 is open and gate G2is shut. The signal S is quantized and coded into the appropriate one of\/1z levels. The gate G1 is then shut and the gate G2 is opened. Theoutput trom the quantizer is fed to the secondary signal generator andthe secondary signal S1 is then subtracted trom the intial signal S.

The diierence so obtained is -then passed to a x/nx amplifier beforebeing applied to the quantizing and coding stage via the -gate G2. Thegate G2 is then closed and gate G1 is opened so that the circuit isready for the next sampling period.

It Iwill be appreciated that the invention is not limited to twoquantizing and coding stages each having r/n levels. For example, it maywell be that it is preferable to code a signal in two stages havingdifferent numbers of levels, i.e. a -level system may have two stages of4 levels and 25 levels respectively. Similarly Ia large nurnber oflevels may be obtained in a system having more than two stages, i.e., 3stages each dealing with levels or alternatively three stages eachhaving a different number of levels.

levels, it is possible to feed back the quantized output in the reflexcircuit `as many times as may be required.

It is to be understood that the foregoing description of specificexamples of this invention is not to be considered as a limitation onits scope.

What I claim is:

1. Apparatus for quantizing and coding individual amplitude samples of asignal wave comprising:

a source of said individual amplitude samples having a predeterminedtime interval between adjacent ones of said individual samples;

an amplitude quantizer means;

a first timed coupling means to couple the output of said source to theinput of said quantizer means during `a first portion of said timeinterval to render said quantizer means responsive to each of saidsamples to produce a first quantized signal at one of a given pluralityof discrete amplitude levels;

a subtraction means coupled to said source and the output of saidquantizer means to produce a difference signal proportional to thedifference between the magnitude of said each of said samples and themagnitude of the associated one of said irst quantized signal;

an ampliiier means coupled to the output of said subtraction meanshaving an amplification proportional to the number of said discreteamplitude levels capable of being produced by said quantizer means;

a second timed coupling means to couple the input of said quantizermeans to the output of said amplier means during a second portion ofsaid time interval sequen-tially related to said lfirst portion torender said quantizer means responsive to said amplied difference signalto produce la second quantized signal at one of said amplitude levels insequence after producing said irst quantized signal;

said rst timed coupling means decoupling the output of said source fromthe input 'of said quantizer means during said second portion and saidsecond timed coupling means decoupling the input of said quantizer meansfrom the output of said ampliiier means during said `irst portion; and

coder means coupled to the output of said quantizer means to code insequence said iirst quantized signal and said second quantized signaland thereby produce a coded output `for said each of said amplitudesamples.

2. Apparat-us according to claim 1, wherein said each of said samples isto be quantized at one of n amplitude levels, Where n equals aninte-ger; and

the amplification of said ampliiier means is proportional to \/n.

3. Apparatus according to claim 1, wherein said each of said samples isto be quantized at one of n amplitude levels, Where n equals an integer;and

said quantizer means is capable of quantizing said each of said samplesand each of said amplied difference signal at one of \/n amplitudelevels.

4. Apparatus according to claim `3i, wherein the amplification of saidampliiier means is proportional to Vit.

References Cited by the Examiner UNITED STATES PATENTS 2,605,361 7/ 1952Cutler 325-38 2,617,879 11/ 1952 Sziklai 328--14 2,949,505 8/1960lKretzmer 340L-345 NE1L C. READ, 'Primary Examiner.

25 THOMAS B. HABECKER, Examiner.

1. APPARATUS FOR QUANTIZING AND CODING INDIVIDUAL AMPLITUDE SAMPLES OF ASIGNAL WAVE COMPRISING: A SOURCE OF SAID INDIVIDUAL AMPLITUDE SAMPLESHAVING A PREDETERMINED TIME INTERVAL BETWEEN ADJACENT ONES OF SAIDINDIVIDUAL SAMPLES; AN AMPLITUDE QUANTIZER MEANS; A FIRST TIMED COUPLINGMEANS TO COUPLE THE OUTPUT OF SAID SOURCE TO THE INPUT OF SAID QUANTIZERMEANS DURING A FIRST PORTION OF SAID TIME INTERVAL TO RENDER SAIDQUANTIZER MEANS RESPONSIVE TO EACH OF SAID SAMPLES TO PRODUCE A FIRSTQUANTIZED SIGNAL AT ONE OF A GIVEN PLURALITY OF DISCRETE AMPLITUDELEVELS; A SUBTRACTION MEANS COUPLED TO SAID SOURCE AND THE OUTPUT OFSAID QUANTIZER MEANS TO PRODUCE A DIFFERENCE SIGNAL PROPORTIONAL TO THEDIFFERENCE BETWEEN THE MAGNITUDE OF SAID EACH OF SAID SAMPLES AND THEMAGNITUDE OF THE ASSOCIATED ONE OF SAID FIRST QUANTIZED SIGNAL; ANAMPLIFIER MEANS COUPLED TO THE OUTPUT OF SAID SUBTRACTION MEANS HAVINGAN AMPLIFICATION PROPORTIONAL TO THE NUMBER OF SAID DISCRETE AMPLITUDELEVELS CAPABLE OF BEING PRODUCED BY SAID QUANTIZER MEANS; A SECOND TIMEDCOUPLING MEANS TO THE OUTPUT OF SAID AMPLIFIER SAID QUANTIZER MEANS TOTHE OUTPUT OF SAID AMPLIFIER MEANS DURING A SECOND PORTION OF SAID TIMEINTERVAL SEQUENTIALLY RELATED TO SAID FIRST PORTION TO RENDER SAIDQUANTIZER MEANS RESPONSIVE TO SAID AMPLIFIED DIFFERENCE SIGNAL TOPRODUCE A SECOND QUANTIZED SIGNAL AT ONE OF SAID AMPLITUDE LEVELS INSEQUENCE AFTER PRODUCING SAID FIRST QUANTIZED SIGNAL; SAID FIRST TIMEDCOUPLING MEANS DECOUPLING THE OUTPUT OF SAID SOURCE FROM THE INPUT OFSAID QUANTIZER MEANS DURING SAID SECOND PORTION AND SAID SECOND TIMEDCOUPLING MEANS DECOUPLING THE INPUT OF SAID QUANTIZER MEANS FROM THEOUTPUT OF SAID AMPLIFIER MEANS DURING SAID FIRST PORTION; AND CODERMEANS COUPLED TO THE OUTPUT OF SAID QUANTIZER MEANS TO CODE IN SEQUENCESAID FIRST QUANTIZED SIGNAL AND SAID SECOND QUANTIZED SIGNAL AND THEREBYPRODUCE A CODED OUTPUT FOR SAID EACH OF SAID AMPLITUDE SAMPLES.